Gecko tape

A new anti-sliding adhesive developed by engineers at the University of California, Berkeley, may be the closest man-made material yet to mimic the toe hairs of the gecko which allow it to move along vertical surfaces and ceilings.

Taking a cue from the millions of hairs covering a gecko's toes, researchers squeezed 42 million hard plastic microfibres onto each square centimetre of a plastic backing material and then loaded it with various weights to test its properties.

They found that on a smooth, clean, vertical surface, two square centimetres of the synthetic adhesive could hold 400 grams (0.88 pounds). At the same time, the adhesive easily lifted off with minimal force and no residue.

A number of research teams across the world are working on mimicking the adhesive properies of the gecko's toes. But Ron Fearing, UC Berkeley Prof of electrical engineering and computer sciences and head of the research team developing the new material, noted that previous research on gecko-like adhesives has only focused on the strength of the adhesion.

He said that the ease of attachment and detachment are equally important when developing a material that could be used in a device that could scale vertical walls and ceilings.

What sets this new gecko-inspired adhesive apart from the others created thus far is that it is directional, only 'sticking' when it slides along a smooth surface, not when it is pressed down.

'This difference is critical because if you're climbing up vertical surfaces, you can't afford to use a lot of energy pressing down into the surface to stick,' said Fearing. 'Using force to attach also requires force to detach. A gecko running uphill may be attaching and detaching its feet 20 times a second, so it'd get very tired if it had to work hard to pull its feet off at every step.'

The structure of the new material is similar to a microfibre array developed by the same research group in 2006. That material relied upon the application of force to make it stick.

'With directional adhesion, however, a gecko can stop itself from falling because the mechanism works without the need for force that is perpendicular to the surface,' said Fearing.

So far, the new adhesive only works on smooth, clean surfaces. The next step, said Fearing, is to develop a material that can also adhere to rough surfaces and that is self-cleaning.